You're pretty much spot-on, Mathias, the background character has the lower body of a spider (or as you put it, arachnacentaur)
It's a specific scene in the story, where Aoi (bird person) grabs Madara's (spider person) shoulders and tells him to go back to sleep. As I imagine it happening in the story, she's looking at Madara, but in the pixel version she's looking at the viewer. I thought it looked cooler that way, like she had some sort of control over him - which she does, in a way.
I noticied some things which I'll fix tommorrow (or later tonight, depending on how late I stay up).